Interspecific somatic cell hybrids retaining the 21st human chromosome will be analyzed by 2-D electrophoresis in order to identify those gene products encoded by chromosome 21. Hybrids retaining and lacking human chromosome 21 will be generated. Gene products of the 21st chromosome will be distinguished from mouse gene products by employing dual-label techniques and computerized analysis. Identified proteins will be studied with regard to subcellular localization, antigenic properties, biochemical characteristics, tissue type distribution, and turnover rates. The activation of liver specific gene product expression from chromosome 21 will be examined. Suppression of gene expression and reactivation following experimental viral infection will be investigated. The proteins identified as mapping to chromosome 21 will be tested for gene dosage effects in monosomy 21 and trisomy 21 cells using quantitative computerized analysis. The effect added superoxide dismutase, a gene product of chromosome 21, has on in vitro growth and senescene of culture monosomy, normal and trisomy 21 fibroblasts will be investigated.